RATHER IRONICALLY, relaxing takes work. Even a do-nothing vacation of cozying up to your Kindle on an uneventful island requires figuring out what to wear for your days in the sun. One garment, however, can help curtail the indecision.

The Off Duty Summer 50

Your guide to mastering the lazy summer

Consider the caftan. “Caftans can be worn on the beach or poolside and then later, perhaps over that same bikini, while you’re having a cocktail at a restaurant,” said Winnie Beattie, owner of Manhattan resort-wear boutique Warm, which offers a variety of loose, wanderlusty styles.

The flowy garments were popularized during the dolce vita 1960s (think: bohemian socialite Talitha Getty on a Marrakesh rooftop), and though they weathered a bleak period in the 1970s as the go-to garment of the dolce-less Mrs. Roper in the sitcom “Three’s Company,” they’re enjoying a renewed vogue.

Last year, Carla Sersale, of the family-run Hotel Le Sireneuse in Positano, Italy, began to offer her line of block-printed cotton caftans, called Le Sireneuse Positano, at retailers beyond the hotel’s shop, such as Bergdorf Goodman. A caftan “can dress you from morning to night,” she said, noting that guests tend to waft from the pool to the terrace restaurant and oyster bar wearing similarly breezy styles. “It’s a very easy garment.”

The process of transitioning from deck chair to dinner, Ms. Sersale and Ms. Beattie agreed, is relatively hassle-free. Just swap flip-flops for strappy heels and throw on some jewelry, whether a pair of dangly earrings, a few layered necklaces or a chunky cuff. The right accoutrements can range from a simple array to the haute bohemian extremes captured in a photo of socialite and style icon Deeda Blair—a caftan inspiration for gallerist Sarah Gavlak. In the photo, Ms. Blair is wearing a scarf-print number “with this incredible long scorpion necklace, and great big sunglasses, and has her gorgeous poodle next to her while she’s sipping a cocktail,” said Ms. Gavlak. As someone who splits her time between Los Angeles and Palm Springs, Ms. Gavlak prefers to wear caftans by the pool, but said she’d go beyond the sun deck: “I would definitely wear one as a hostess outfit. It’s casual, but you’re in a gown, in a way.”

Before accessorizing, however, it’s important to choose the right one. Caftans can easily go awry: swallowing a small frame, bulking up a larger one, or reading more tent than Talitha. “Some women feel better if they have a bit of ankle showing,” said Warm’s Ms. Beattie. Petite women, she added, might consider a sleeveless caftan or one with a lower neckline. Ms. Sersale recommended a style with side-slits to show off a bit of leg. “It breaks up the shape and makes it more graceful,” she said.

Chic prints or stripes are enough to make an impact; heavy beading can overdo it for day. “I think embellished caftans are fabulous, but sometimes they’re overpowering,” said Vogue editor-turned-designer Pippa Holt, who enlists Mexican artisans to hand-weave her new cotton caftan collection. Find the caftan that best suits you, and you’ve cracked the vacation-dressing code—with a healthy side of glamour. “It’s a dream statement,” said Ms. Sersale. “You feel empowered to be Sophia Loren.”